endurance/energy curve?

tell me if it's just me, or does anyone else have this"prob". my warmups consist of say 6 light, 4 med.,& 1 or 2 heavier reps. any more than this & my total load is going to drop pretty rapidly. i'm trying not to get injured & have been fairly lucky. but my fatigue seems to come on quickly. i just can't ( & won't ) do the 1 1/2 hr sessions. 45 minutes is a large amount of volume to me. i tried some edt, though pumping weights even pushing then pulling sets for 15-20 minutes without a real break really difficult & i end up with really light weights to keep it up. i seem to gravitate to say 5 rep sets. if not 1 or 2. maybe just dominately fast twitch?i want to do alot of volume, especially while "on". i'm thinking maybe just more sets? anybody else experience this sort of thing?